This invention relates to an uncovered storage facility for stockpiling bulk materials. The invention is particularly applicable to an import or export terminal for bulk materials and will be described mainly in relation thereto, but it is to be understood it is applicable to any facility providing a stockyard for bulk materials. Examples of bulk materials commonly stored in such facilities include coal, iron ore, limestone and bauxite.
In typical export terminals, materials arrive by road or rail transport and are loaded into ships holds whereas at typical import terminals the reverse occurs. As the volumes handled by road or rail shipments are much smaller than those handled by a ship, and given that materials may not be received at the time they are needed for loading, a buffer of the materials is usually established in stockpiles in a stockyard at the import or export (or intermodal) terminal. Such stockyards generally involve large land areas and the provision of facilities for handling the bulk materials between their arrival at a terminal and their delivery from the terminal. Such facilities generally involve receiving, stacking, blending, reclaiming etc of the materials.
Due to the nature of Bulk Materials Handling, these terminals tend to be quite large. For example xe2x80x9clarge volumexe2x80x9d terminals may handle in the order of 1,000,000 to 100,000,000 tonnes of throughput per annum (examples in Australia are coal export terminals at Newcastle in New South Wales, Gladstone in Queensland and Drylmple Bay and Hay Point at Makay in Queensland; iron ore export terminals at Dampier and Port Headland in Western Australia; and the cement clinker facility at Gladstone in Queensland). xe2x80x9cMedium Volumexe2x80x9d terminals may handle in the order of 10,000 to 10,000,000 tonnes per annum.
Known import or export terminals, which provide facilities for stockpiling bulk materials, are generally purpose built to handle only one or two types of material, or materials for a particular industry.
The present invention provides a stockpile facility for a terminal for s tacking, storing and reclaiming materials in which economies are achieved by its compactness allowing an efficient utilisation of machinery and by its flexibility in its use for a multitude of materials.
The efficiency of operation of a bulk materials terminal is optimised by appropriately matching all its operations generally in relation to an intended throughput capacity and the method of operation. There are two main methods of operation, namely xe2x80x9ccargo assemblyxe2x80x9d and xe2x80x9cbulk material bankingxe2x80x9d, and they have different requirements for material buffering and thus stockpile sizes between delivery of a bulk material to the stockpile facility and its departure therefrom.
Cargo Assembly involves delivery of minimum bulk material to an export terminal on a just-in-time basis to fill the cargo requirements of a ship being expected in the port within a certain time frame, typically three to eight days. That is, the deliveries begin at a sufficient time in advance of the bulk material being needed for loading to build a sufficiently large buffer for the particular ship to be loaded without interruptions. The arriving material may be stacked in and reclaimed from several distinct stockpiles because blending may be required during loading (involving reclaiming from multiple stockpiles) or because the ship is to be loaded with a multiple of distinct cargos. Generally the stockpiles with this method are relatively small.
Bulk Material Banking involves delivery of bulk materials to an export terminal on a regular basis and maintenance in a stockyard of a minimum inventory of a given material or grades and blends thereof. The minimum inventory is typically a specified percentage of the annual or monthly throughput of the given material. Generally this involves the stacking of all cargoes for all ships of the given material together in a minimum number of distinct stockpiles, rather than stacking each cargo for each ship. Thus with this method the stockpiles are significantly larger than for the cargo assembly method.
The present invention seeks to provide a stockyard facility which caters for and achieves efficiencies primarily in relation to Bulk Material Banking. However it may be beneficially usedxe2x80x94and flexibly over timexe2x80x94for either Cargo Assembly, or Material Banking, or Cargo Assembly together with Material Banking.
Principal determinants of the capital, operating and maintenance costs of an import or export terminal are
the boom lengths for the mobile stackers and reclaimers (the cost and mass, and therefore wear and tear, of these machines is proportional to the square of the length of their booms),
the throughput capacity ratings for each of the machines and conveyors.
length (and width) of stockyard for a given storage capacity.
The layout and dimensions of the stockyard in a terminal has a significant influence on these determinants. For example the pad width, that is the width of a stockpile, relates to the boom length of the reclaimers and stackers. Generally the total volume of stockpile that is needed is sized according to the intended number of distinct stockpiles needed to accommodate distinct materials or material owners, throughput capacity and method of operation (that is, Cargo Assembly or Bulk Material Banking). A cross-sectional size for the stockpiles is then chosen to optimise between the angle of repose of the bulk materials to be stored and the horizontal (and secondarily the vertical) operating range for the stacker and reclaimer machines. These parameters define the total pad length (and therefore area) needed which must also be sized to allow for unhindered operation between stackers and reclaimers servicing individual stockpiles. The total pad length and area, and volumetric capacity, can then be satisfied as either a single and/or a multiplicity of pads. Clearly, the provision of a stockyard requires a large area of land and an arrangement which minimises that land requirement-without compromising the efficiency of the stockyard operations is highly desirable, particularly where large parcels of land suitably located are scarce.
The capital, maintenance and operating efficiency of a stockyard depends on several parameters. For example, narrower stockpiles allow for shorter boom lengths for the stacker and reclaimer machines and thus lower capital, maintenance and operating costs. Shorter length stockpiles allow shorter rails (on which the stackers and reclaimers move), shorter conveyors and related civil works and thus reduced capital, maintenance and operating costs. Shorter stockpiles also lead to reduced re-locating distances for the machines and thus reduced operating and maintenance costs for them, and thus may also reduce the delay times and thus costs in receiving/unloading/stacking bulk materials and in reclaiming/loading/despatching the bulk materials. Other factors relate to the pattern with which a stockpile is stacked (for example, windrow stacking, coneplying or chevron stacking) which can affect the uniformity of recovery of material from a stockpile by a reclaimer machine. The uniformity of material recovery is also affected by the reclaiming method, three of which are commonly used, namely (i) the slew bench cut and pilgrim step, (ii) travelling bench cut and (iii) combined slew and travel bench cut. None of these methods allows the reclaimer to always reclaim at a uniform rate.
A stockpile for which a given volume is presented with a predetermined and more generally rectangular cross-section (compared with a more triangular cross-section of a traditional stockpile) represents a stockpile for which each relative sub-cross section presented to the reclaimer bucket wheel and for which the average of all sub-cross sections presented to the bucket wheel have a higher material to void content than traditional stockpiles. This results in both more effective reclaiming (ie. the reclaimer is able to more often encounter a higher material to void cross-section over the course of reclaiming a stockpile) and less variation in the reclaim rate (ie. less deviation in the differences between material to void cross-sections encountered over the course of reclaiming a stockpile) and thereby a higher effective reclaim rate achieved resulting in a greater operating efficiency for both the reclaimer, and thereby enabling the reclaimer to load the take-away conveyor closer to full on a time average basis, providing for a greater operating efficiency for the conveyor. Hence, for both the reclaimer and for the take-away conveyor system (all the way to its destination), lower capital, maintenance and operating costs are achieved.
The present invention seeks to provide a facility for stockpiling bulk materials for realising an optimal operating efficiency.
In summary, the invention provides a facility which includes means for establishing a predetermined stockpile geometry that is more generally rectangular in cross-section than conventional more triangular cross-section stockpiles, which means also provide for more efficient access to the stockpile and function by a stacker and a reclaimer.
According to the invention, an uncovered storage facility for stockpiling bulk materials includes a base and facing retaining walls for containing a stockpile of a bulk material having a length in the direction of the retaining walls, wherein each retaining wall is defined by a berm for supporting, respectively, a stacker and a reclaimer machine for the stockpile for movement along the length of the stockpile.
In this description and the following claims, the word xe2x80x9cbermxe2x80x9d is to be understood as meaning a structure which provides an upright surface (that is, the retaining wall surface) and an upper surface on which a stacker or reclaimer machine is locatable.
Preferably one retaining wall is higher than the other, wherein the berm defining the higher retaining wall is for supporting the stacker and the berm defining the lower retaining wall is for supporting the reclaimer.
Thus a stacker is positionable on one side of the stockpile and a reclaimer on the other on berms which also provide retaining walls for the stockpile. The retaining walls allow the establishment of a stockpile of reduced base area to volume ratio (ie with a more generally rectangular cross-section) compared to traditional stockpiles having sides which slope with the material""s characteristic angle of repose down to ground level (ie which have a more triangular cross-section). The stockpile that is established to realise the advantages of the invention extends above the retaining wall and is, where possible, made flat topped, thus its sides slope downwardly away from its flat top at the characteristic angle of repose of the material down to the retaining walls. This geometry, hereinafter referred to as a compact stockpile, in addition to providing shorter and narrower stockpiles for a given volumetric capacity also assists in reducing variations in reclaim rate which occur when a traditional stockpile is reclaimed. That is, it provides a stockpile for which each relative sub-cross-section presented to the reclaimer bucket wheel and for which the average for all sub-cross-sections presented to the bucket wheel have a higher material to void content than traditional stockpiles.
Preferably the facility provides side by side bases separated by berms for containing a plurality of substantially parallel extending stockpiles separated by the berms, wherein a berm for a reclaimer alternates with a berm for a stacker. The side-by-side stockpiles may be substantially straight lengthwise, or curved according to a large radius. The reclaimer and stacker machines travel on rails on the berms parallel to or concentric with the axes of the stock piles.
The arrangement of the stackers and reclaimers between the stockpiles in an alternating fashion enables one of the two alternating berms to be not height limited by the maximum functional angle of reclaimer boom operation as well as facilitates unhindered operation between stackers and reclaimers.
Fundamental parameters for the facility are the transfer rates to and from a stockpile. The transfer rate from the stockpile (that is, the reclaiming rate), determines the size of the bucket wheel of a reclaimer, which in turn determines the practical height options for the stockpile.
A stockpile is nominally divided into a number of benches, wherein each bench is the layer that a reclaimer machine reclaims at a particular angle for the boom of the machine, and the height of which depends on the depth of the cut. For a safe and efficient cut, the depth thereof is typically just greater than the bucket wheel radius. Because material tends to fall out of the buckets on the upper benches and into the buckets on the lower benches the cutting depth can be increased at the higher benches, but is generally decreased at the lower benches. The stockpile height is then the accumulation of the benches chosen. Typically, a traditional triangular cross-section stockpile consists of four benches, for example, for a bucket wheel diameter of Dw and from top to bottom of the stockpile, bench 1=0.8 Dw, bench 2=0.7 Dw, bench 3=0.6 Dw and bench 4=0.5 Dw, giving a stockpile height of 2.6 Dw.
A compact stockpile for realising the advantages of the invention preferably is reduced in height by about the depth of the top bench (thus giving the flat top) and the height of the higher berm, which is for supporting the stacker, is optimally up to about the boundary between the upper and middle benches of the three benches that remain. Thus the stockpile height h1 may be about 1.8 Dw and the height h2 of the high berm about 1.1 Dw. Expressed in terms of the width d of a stockpile, the height h1 may be about 0.35 d and the height h2 about 0.2 d. Preferably, for a stockpile having a base width d between the retaining walls, and for a reclaimer having a bucket wheel of diameter Dw at the end of a pivotal boom which carries a conveyor for receiving the bulk material from the bucket wheel, the maximum height h3 of the berm for supporting the reclaimer is defined by the relationship
h3=dxc2x7sin(xcex3)+xc2xdxc2x7Dwxe2x88x92S3
where
xcex3=the angle of maximum inclination of the conveyor of the boom, and
S3=the minimum structural height of the reclaimer for it to support the pivotal boom.
In terms of the width of a compact stockpile, height h3 may be about 0.06 d. A compact stockpile geometry as above described significantly increases the stockpile cross-section per stockpile pad (base) width, the capacity of the stockpile pad per given length, the overall stockyard capacity per given length and width, and thereby reduces capital, maintenance and operating costs for a terminal for principally, the Bulk Material Banking method of operation and secondarily for the Cargo Assembly method of operation. This is because Bulk Material Banking involves relatively few large stockpiles and few smaller stockpiles which do not fill the predetermined cross-section, while Cargo Assembly involves relatively many stockpiles, including small stockpiles which do not fill the predetermined cross-section. The Cargo Assembly case, with its greater number of xe2x80x9cend conditionsxe2x80x9d (stockpile ends which conform to the angle of repose) and small stockpiles not filling the predetermined cross-sections, requires a greater total void volume compared to occupied volume of material storage capacity in the stockyard. The occupancy of a given quantity of material in Bulk Material Banking mode requires less stockyard capacity than the same quantity in Cargo Assembly mode. With its use of berms and the provision of retaining walls thereby to contain the compact stockpile crosssection, the invention offers significant efficiency improvements over the use of traditional stockpiles via, among other things, reduced stacker and reclaimer machine relocation times, higher achieved stacking and reclaim rates and more efficient use of the conveyor systems.
For a better understanding of the invention, embodiments thereof will now be described, by way of non-limiting example only, with reference to the accompanying drawings.